1. Field of the Invention
The present invention relates to a touch screen device in which a fingertip of the user, or the like, is pressed against the surface of a touch panel, and an input operation is thereby performed, and more specifically, it relates to a touch screen device in which feedback using sense of touch to the user can be performed by vibrating the touch panel at the time of input operation.
2. Description of the Related Art
When a touch screen device having a feedback mechanism that vibrates a touch panel at the time of input operation detects that a fingertip or the like of the user is pressed against any place or a predetermined area of the surface (input operation surface) of the touch panel, an actuator that is a vibration generation source is activated and minutely vibrates the touch panel. For example, when a fingertip or the like of the user is pressed against the input operation surface of the touch panel, the device detects this and vibrates the touch panel. The vibration is transmitted to the fingertip or the like, and the user can sense that input operation is being performed without fail. When it is detected that a fingertip or the like of the user is pressed against a particular area of the input operation surface (an area in the image on the display panel where selection items are displayed), the touch panel is vibrated in a vibration pattern corresponding to the particular area. This makes it easy to prevent erroneous operation.
In general, a piezoelectric element, a motor with an eccentric weight, or an electromagnetic actuator is used as a vibration generation source in this type of touch screen device (see, for example, Japanese Unexamined Patent Application Publication No. 2005-275632). When the vibration generation source is a piezoelectric element, the touch panel can be directly vibrated. A motor with an eccentric weight is often used as a vibration generation source in cell-phones or the like. The touch panel is vibrated by rotating the eccentric weight with a small cylindrical motor. When an electromagnetic actuator is used as a vibration generation source, the touch panel is vibrated by vibrating a movable coil or the like in a magnetic circuit.
However, when a piezoelectric element is used as a vibration generation source of a touch panel, the cost of the touch screen device increases because the piezoelectric element is expensive and a booster circuit or the like needs to be provided. In addition, since the driving force generated by a piezoelectric element is small, using a piezoelectric element as a vibration generation source in order to vibrate a touch panel with a high acceleration (for example, about 5 G) is inefficient and is not practical.
When a motor with an eccentric weight is used as a vibration generation source of a touch panel, the cost is reduced, but the amplitude in the desired direction of vibration is not stable because the vibration is generated by the rotation of the eccentric weight. The user easily recognizes the vibration of the touch panel in the thickness direction thereof (direction perpendicular to the input operation surface), and it is effective to vibrate the touch panel in this direction. However, when a motor with an eccentric weight is used, the vibrating direction of the touch panel varies, and therefore it is difficult to efficiently vibrate a touch panel having a somewhat large screen. If a large and powerful cylindrical motor is used, the touch panel can be vibrated with a high acceleration. However, in this case, the thickness of the touch screen device increases undesirably.
When an electromagnetic actuator is used as a vibration generation source of a touch panel, the thickness of the touch screen device increases owing to the magnetic circuit. In this case, a very large magnetic circuit needs to be incorporated in order to vibrate the touch panel with a high acceleration. Therefore, the thickness of the touch screen device is significantly increased.